1. Field of the Invention
The present invention relates to a nitride semiconductor laser element and to a method for manufacturing this element, and more particularly relates to a nitride semiconductor laser element that exhibits good reliability even when driven continuously in a high-output state, and to a method for manufacturing this element.
2. Background Information
A nitride semiconductor is formed from an InxAlyGa1−x−yN (0≦x, 0≦y, 0≦x+y≦1) compound semiconductor, and a semiconductor laser element made from this semiconductor is increasing uses in next-generation DVDs and other such optical disk systems capable of high-capacity, high-density information recording and reproduction, and in personal computers and other such electronic devices, as well as is continuing to rise in applications such as light sources for optical networks, laser printers, and so on because it is believed to be capable of oscillation over a wide band of visible light wavelengths, from the ultraviolet band to the red band. Accordingly, semiconductor laser elements that make use of nitride semiconductors have been the subject of a great deal of research.
For example, the bandgap energy of a nitride semiconductor decreases when an impurity state is formed on resonator end faces, so outputted light is absorbed at resonator end faces formed by cleavage or RIE (reactive ion etching), and this absorption generates heat at the resonator end faces. The heat that is generated raises the temperature at the resonator end faces, decreases the bandgap at the resonator end faces, and increases the absorption of outputted light. This results in catastrophic optical damage (COD) to the end face.
Consequently, to obtain a laser with high output, it is very important to suppress the generation of heat at resonator end faces by suppressing the absorption of light at the end face.
One proposal aimed at this goal is a method for forming a window structure in a nitride semiconductor laser element, or forming an AlGaInN semiconductor film as a protective film for an end face (such as Japanese Laid-Open Patent Application H7-249830).
Also, as shown in FIG. 9a, a laminated semiconductor structure (11, 12, 13) of an optical device is formed, after which ions 37 are implanted in a contact layer disposed on the surface of the laminated structure near resonator end faces 30, and as shown in FIG. 9b, a current non-implantation region 33 is formed to form an optical non-absorption region in the resonator end faces 30 (such as Japanese Laid-Open Patent Application 2002-261379).
With these methods, however, it is difficult to adjust the beam shape of the laser outputted from the resonator end faces, or the active layer is damaged during the manufacturing process, for example, so it is still impossible to adequately maintain the characteristics at the resonator end faces while preventing end face deterioration.